Corrective heating of pneumatic tires

ABSTRACT

Adverse effects on pneumatic tire performance caused by an excessive variation in radial force are reduced by localized heat treatment of the cured pneumatic tire. The area where an excessive variation will occur is determined and the tire is suspended on a special heating fixture with its axis of rotation disposed horizontally such that said area is located vertically above the axis. Heat is applied to a portion of the inner surface of the tire adjacent said area for a predetermined time and/or until a predetermined maximum inner surface temperature is reached. This treatment results in a reduction in the magnitude of the force variation.

United States Patent Brown et al..

[451 Mar. 18, 1975 James D. Farris, all of Mayfield, Ky.; John A. Feola,Akron, Ohio [73] Assignee: The General Tire and Rubber Company, Akron,Ohio are 3,632,701 1/l972 Devitt et al. 264/100 X Primary Examiner-JanH. Silbaugh [57] ABSTRACT Adverse effects on pneumatic tire performancecaused by an excessive variation in radial force are reduced bylocalized heat treatment of the cured pneumatic tire. The area where anexcessive variation will occur is determined and the tire is suspendedon a special heating fixture with its axis of rotation disposedhorizontally such that said area is located vertically above the axis.Heat is applied to a portion of the inner surface of the tire adjacentsaid area for a predetermined time and/or until a predetermined maximuminner surface temperature is reached. This treatment results in areduction in the magnitude of the force variation.

2 Claims, 3 Drawing Figures PATENTEU 1 8 9 5 SHEET 2 2 1 V CORRECTIVEHEATING OF PNEUMATIC TIRES BACKGROUND OF THE INVENTION This inventionrelates to improvements in pneumatic tires and particularly toimprovements in the riding characteristics of pneumatic tires.

A pneumatic tire rotating under load against a surface, such as aroadway, generates variable forces against that surface throughout onerevolution. This phenomenon is caused by a great number of factors whichthe tire industry usually collectively calls tire non-uniformities.These variable forces can each be described as a composite of a radiallateral and tangential force component each of which force componentsare also variable throughout one revolution.

It is a widely accepted view that the variable radial force component(hereinafter radial force variation) has a significant effect upon theriding characteristics of pneumatic tires. Studies have been made whichconclude that tires which generate radial force variations which exceedcertain magnitudes have undesirable rid ing characteristics.

In recent years many attempts have been made to solve this problem themost successful of which has been the development of methods andapparatus directed toward force correction" of these tires.

Force correction basically includes correlating an area or areas of thetire with the potential generation of a force variation or variations(usually radial) of excessive magnitude and. doing something to' thattire which reduces the magnitude to an acceptable value.

Specific corrective methods and apparatus of this type vary and notablyinclude those based upon the removal of small amounts of material fromthe tire, the addition of small amounts of material to the tire, or thecontrolled reheating of tires.

Force correction based upon the removal of material from the tire(hereinafter corrective grinding) is disclosed in U.S. Ser. No. 613,252filed Feb. 1, 1967 now abandoned in favor of a continuation applicationU.S. Ser. No. 73,602 filed Sept. 18, 1970 and a divisional U.S. Ser. No.18,773 filed Feb. 27, 1970, now U.S. Pat. No. 3,724,137, all of whichare assigned to the present assignee.

Force correction based upon the adding of material to the tire(hereinafter corrective addition) is disclosed and claimed in U.S. Ser.No. 57,384 filed July 21, 1970, now abandoned, which is acontinuation-inpart of the aforementioned U.S. Ser. No. 613,252 andwhich is also assigned to the present assignee.

Force correction based upon the controlled reheating (hereinaftercorrective heating) is disclosed in U.S. Ser. No. 874,686 filed Nov. 6,1969, abandoned in favor of continuation-in-part U.S. Ser. No.- 61,819filed Aug. 6, 1970 which issued as U.S. Pat. No. 3,632,701, alsoassigned to the present assignee. Corrective heating includes analyzingthe tire to locate the area which correlates with the potentialgeneration of an unacceptable radial force variation and suspending thetire such that its axis of rotation is disposed horizontally and thelocation of said area is vertically above the axis of rotation andheating the tire, while suspended in this manner, for a predeterminedperiod of time to effect a reduction of the magnitude of the radialforce I variation.

Excessive force variations in some cases, should be reduced bycorrective grinding only when the magnitudes are not overly excessive.In other words, there is a practical upper limitation on the magnitudesof excessive force variations which permit corrective grinding. Tireshaving radial force variation magnitudes which exceed this limitationshould not be corrected by present corrective grinding techniques.Accordingly, however, corrcctivc heating may be used prior to correctivegrinding to reduce an overly excessive force variation to the levelwhere further reduction by corrective grinding is then permissible.

Thus corrective heating may be used singularly to reduce excessive forcevariations to an acceptable level or in conjunction with correctivegrinding to reduce overly excessive force variations to a levelpermissible for corrective grinding.

Presently, corrective heating processes such as those disclosed in U.S.Pat. No. 3,632,701 have several problems associated therewith. Theprocesses involve unusually long periods of time (usually more than tenminutes per tire). Also, the equipment used in certain of the processescan be cumbersome, inefficient and often impractical from the standpointof commercial production.

The present invention is concerned with an improved corrective heatingprocess.

SUMMARY OF THE INVENTION It is an object of the present invention toimprove upon known corrective heating processes performed upon curedpneumatic tires.

It is another object of the present invention to provide an improved,relatively simple and efficient method for heating a tire to reduceundesirable force variation generated by a tire when rotated and underlower load against a surface.

These and other objects, which will become evident hereinafter, areachieved by the method according to thepresent invention wherein a tireto be corrected is suspended in an upright position such that its axisof rotation is substantially horizontal and a previously located area ofhigh radial force variation is disposed substantially vertically abovesaid axis and while the tire is so disposed heat is directed or focusedupon a portion of the inner surface of the tire adjacent said area for aprescribed period of time and/or until said portion of the inner surfacereaches a prescribed maximum temperature.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a side elevation of a preferred embodiment of the apparatusaccording to the present invention;

FIG. 2 is a frontal view of the apparatus shown in FIG. 1 with certainportions broken away and/or omit ted;

FIG. 3 is an enlarged sectional view taken along lines 3-3 of FIG. 2.

DETAILED DESCRIPTION AND A PRESENTLY PREFERRED EMBODIMENT OF THEINVENTION Referring to FIGS. 1 through 3 the apparatus of the presentinvention according to a presently preferred embodiment includes avertically disposed support member 10 including a support post 11 and abase 12 bolted or otherwise secured to the floor, foundation or thelike. The support post 11 may be cylindrical as shown or any otherdesired configuration found suitable. The support post material shouldbe of adequate strength such as steel. Furthermore, it is evident thatfor reasons of convenience or space requirements vertical supports otherthan that shown may be used such as, for example, a vertical wall. Also,if desired, the apparatus may be made portable by suitable attachment ofvertical support to a movable platform.

Welded or otherwise secured to the upper end vertical support post 10 isa horizontal support member or arm extending in cantilever fashiontherefrom. When required, support of arm 20 by post 11 may be bolsteredby a triangular brace or gusset 16 as shown. Horizontal support member20 maybe a cylindrical steel member or any other desired configurationand/or suitable material. Also, if necessary, a part of the lowerportion of arm 20 such as indicated at 26, may be removed to reduce theweight-to be supported.

A heating means is mounted on horizontal member 20 by a spaced pair ofsuitable mounting plates 22. The heating means 30 preferably includes aninfra-red heating device 32 disposed within an open ended case composedof two parallel side plates 24 and a flat bottom plate 26 welded orotherwise secured to mounting plates 22. An arcuate seat 34 is welded orotherwise secured to each pair of opposite upper ends of the parallelside plates 24. Welded or otherwise secured to each arcuate seat 34 andto the upper edges of side plates 24 is an upwardly extending flange 36.The infra-red heating device 32 is a commercially available device andusually includes one or more quartz infra-red lamps such as 38 (FIG. 3)and typical or conventional deflectors (not shown).

Welded or otherwise secured to the horizontal arm 20 is a conventionaltimer switch 40 which permits or prevents the passage of electricalcurrent from a suitable source (not shown) to the heating device '32through appropriate wiring 42. An on-off switch 44 opens or closes thecircuit to heating device 36 and when the circuit is closed a timer maybe set which automatically opens the circuit after a pre-set lapse oftime. 1

As described in the aforementioned US. Pat. No.

3,632,701 corrective heating and, therefore, the process in accordancewith the present invention which is an improvement thereof, findsparticular advantages when utilized on tires which have beenpost-inflated. Briefly, post-inflation is a process whereby tires uponremoval from the curing press are inflated to a prescribed pressure on arim and allowed to cool to a preselected temperature. This postinflation reduces any tendency which the tire reinforcement cords haveto shrink upon cooling and re-elongate during use. This tendency is moreprevalent in tires utilizing nylon and- /or polyester type cords.

Post inflation, however, has been found to have an adverse effect uponthe uniformity of the tire as determined by the magnitudes of radialforce variations generated when the tire rotates under load against asurface.

These radial force variations are typically determined by means such asthose described in US. Pat. No. 3,632,70l and those'tires found to havean excessive or unacceptable force variation or variation are eithercorrected by techniques previously described or are reclassified.

Although ranges of uniformity classifications of force measured tiresmay vary, a typical example of a passenger tire which would not needcorrected, or in other words would be considered uniform, would be onewhich is determined to have no radial force variation in excess of 25pounds. Passenger tires generating one or more force variations of amagnitude of between about 26 to 45 pounds might, then, for example, be-

considered within the permissable to grind" limits previously mentioned.Further, passenger tires generating a radial force variation in excessof 45 pounds would, then, in some cases not be considered for correctivegrinding.

The specific force values mentioned above are based upon what is oftenreferred to as the radial composite or peak to peak force variation. Acurve (sometimes called a uniformity curve) plotting radial forcemagnitude vs circumferential tread locations for one revolution of thetire is composed of summation of harmonic curves. Therefore, a radialforce variation can be considered as a composite of many harmonic forcevalues. It is widely accepted that the first harmonic curve is theprincipal contributing factor to the radial composite force curve. Underthis view, tires are now sometimes analyzed by determining the locationof the peak of the first harmonic curve and corrected if that peakexceeds a predetermined limit.

In accordance with the prec'eeding, tires may be appropriately marked tolocate an excessive radial composite force variation or excessive radialharmonic force, or both. After a tire has been marked as nonuniformindicating an excessive radial first harmonic or composite force orboth, it is then desirable to correct this tire. The the may becorrected by corrective heating or corrective grinding or both asdisclosed in US. Pat. No. 3,632,701.

In corrective heating, the tire is suspended in an up right positionsuch that its axis of rotation is substantially horizontal and the markor location indicative of an excessive radial force variation (eitherharmonic or composite) is substantially vertically above said axis.While in this position the tire is heated and a reduction in theexcessive force variation results to the extent that corrective grindingis not necessary or is thereafter permitted if thetire had originallybeen outside the permissible to grind limits..

As aforementioned, prior corrective heating techniques have thus farrequired impractical periods of time. Also, in some cases, inflation ofcertain tires on rims is necessary to, achieve desired results. Further,prior corrective heating processes require cumbersome equipment such asovens, pot heaters and/or autoclaves.

In accordance with this invention it has been discovered that byaltering the manner whereby heat is applied to the tire duringcorrective heating processes, the disadvantages mentioned becomenon-existant. Specifically, by directing heat only toward that portionof the tire inner surface adjacent the location indicative of anundesirable radial force variation, the corrective heating time may besignificantly reduced, inflation of certain tires becomes unnecessary,and the equipment used is greatly simplified.

The present invention may be more readily understood by describing theprocess in a preferred form utilizing the apparatus previously describedin detail and shown'in the accompanying drawings.

A tire T with a mark M (see FIG. 2) which indicates the circumferentiallocation indicative of an excessive radial force variation (eithercomposite or first harmonic) is placed upon horizontal support arm suchthat flanges 36 fit between the two annular bead portions B of tire T.the radius of curvature of arcuate seats 34 is generally the same as theradius of curvature of the bead portions B so as to lessen the chancesof injury to the bead portions during placement of the tire. As can beseen, the tire T is mounted so that it is suspended above the floor orfoundation and its axis of rotation is generally horizontal. Also, thetire is angularly disposed such that the mark M is substantiallyvertically above this axis of rotation. Heat is then applied verticallyupwardly as indicated by the direction of arrow A directly to a portionP of the inner surface S of the tire T, which portion P is adjacent thelocation M indicative of the excessive force variation.

The inner surface of most tires include a thin layer of elastomericmaterial usually called an inner liner which covers the cord reinforcedcarcass. Tests have shown that the temperatures achieved at these innerliners during corrective heating may be used as controlling parametersassociated with the corrective heating proce'ss of this invention. Forexample, for most passenger and light truck tires having polyester ornylon carcasses it is found that when the portion of the inner linertoward which heat is directed reaches a temperature between 225 to about240F., a reduction in radial force variation to a desirable levelresults. However, it has been found in some of these tires that furtherheating to inner liner temperatures substantially above 240F. mayadversely affect the tire dimensionally.

This limitation on inner liner temperature can of course vary withsubstantive differences in inner liners. The thickness and compositionof the inner liner for example, can directly influence this temperaturelimitation.

Controlling the corrective heating process of this invention with,regard to the inner liner temperature achieved is, however, somewhatimpractical. This would require that appropriate temperature sensors,such as thermocouples, be connected to each tire heated. Fortunately,most pneumatic tires may be generally categorized according to typesand/or size ranges. Tires within such categories are fairly standardizedand thus somewhat similar. By determining the maximum inner linertemperature limitation of tires within a certain category andcorrectively heating a series of tires of such category, it is possibleto associate an accurate criterion of maximum corrective heating timewith the attainment of the maximum inner liner temperature limitation.Thus, depending upon the manner by which heat is applied, practicaloperating criteria may be established based upon heating time.

As stated previously, heat correction of typical polyester or nylonpassenger or light truck tires is usually achieved at an inner linertemperature between about 225F. and 240F. Using 240F. as an arbitraryupper temperature limit for the inner liner and using an infraredheating device of the type described herein such an inner linertemperature is normally achieved between about 2% to 3 minutes. Thistime can, of course, vary with tires having substantial differences insection height. Thus tires with relatively small or low section heightsmay only require heat times slightly less than 2 minutes, while tireswith relatively large or high section heights might require heat timesslightly beyond 3 minutes.

To exemplify the above-corrective heating timcs. Table I evaluateschanges in radial force variation of a given size tire at selected timeintervals up to about 8 minutes using an infra-red heating device asdisclosed herein. The values of force variation change listed representan average of 5 tires for each time interval except that for 8 minuteswhich included only two tires. The subjective Comments" relates to anynoticeable distortion of the tire.

From this data it was observed that at times beyond 4 minutes the radialcomposite force variation began to increase rather than decrease. Also,from the Comments it is seen that although at times beyond 3 minutesradial composite force variation did decrease, the dimensionalregularity of the tires was adversely affected and hence were Notacceptable.

After this experiment 9 tires similar to those tested in Table l wereheat corrected by the same device using heat times of 2% minutes. Theaverage reduction in radial composite force variation for these 9 tireswas 7.6 pounds, while the radial first harmonic average reduction was8.4 pounds. All 9 tires remained acceptable with regard to dimensionaldistortion.

These optimum heat times can also vary with alternative manners of heatapplication. As suggested previously, heating by an infra-red heatsource is preferred, but not absolutely necessary. Accordingly, heat maybe applied to the portion of the inner liner adjacent the undesirableforce variation in other ways, if desired,-

such as by directing hot air or steam toward such portion.

Thus, by establishing proper corrective heating times, the process canbe operationally controlled by suitable timers such as that shownassociated with the apparatus described above.

As mentioned above, an important facet of the corrective heating processis its use to increase a manufacturers Yield of uniform tires bycombining corrective heating with other correction techniques such ascorrective grinding. Thus corrective heating can be used to reduceexcessive force variations to a level where corrective grinding ispermissable. Recalling that under typical uniformity classifications orstandards discussed above, tires found to have an excessive radialcomposite force variation exceeding 45 pounds are sometimes not normallycorrected by grinding, and tires having such variations of 25 pounds orless are considered uniform. Under Table ll which follows, twelvetypical polyester reinforced tires were selected, including passengerand light truck types, all of which had radial composite force variationoutside the "permissible to grind" limits. Table [I demonstratescorrection of these tires utilizing a combination of corrective heatingaccording to this invention and corrective grinding. The heat times onall tires were 2 /2 minutes.

Although the apparatus and process of the instant invention have beendisclosed in presently preferred forms, 'it is understood thatvariations from what has been specifically described in the foregoingmay be made which fall within the scope of the appended claims.

What is claimed is:

1. In the method of heat treating a cured pneumatic tire suspended in anupright position such that the axis of rotation of said tire issubstantially horizontal and an area indicative of an undesirable radialforce variation is located substantially vertically above said axis, theimprovement wherein said heat treating, which results in a reductioninthe magnitude of said force variation without adversly affecting thedimensional regularity of the tire, comprises applying heat directlyonly upon a portion of the inner surface of said tire adjacent said areauntil said inner surface reaches a maximum predotermined temperature notto substantially exceed about 240F.

2. The improvement defined in claim 1 wherein said heat is directed uponsaid inner surface for a predetermined period of time not tosubstantially exceed about 3 minutes.

1. IN THE METHOD OF HEAT TREATING A CURED PNEUMATIC TIRE SUSPENDED IN ANUPRIGHT POSITION SUCH THAT THE AXIS OF ROTATION OF SAID TIRESUBSTANTIALLY HORIZONTAL AND AN AREA INDICATIVE OF AN UNDESIRABLE RADIALFORCE VARIATION IS LOCATED SUBSTANTIALLY VERTICALLY ABOVE SAID AXIS, THEIMPROVEMENT WHEREIN SAID HEAT TREATING, WHICH RESULTS IN A REDUCTION INTHE MAGNITUDE OF SAID FORCE VARIATION WITHOUT ADVERSLY AFFECTING THEDIMENSIONAL REGULARITY OF THE TIRE, COMPRISES APPLYING HEAT DIRECTLYONLY UPON A PORTION OF THE INNER SURFACE OF SAID TIRE ADJACENT SAID AREAUNTIL SAID INNER SURFACE REACHES A MAXIMUM PREDETERMINED TEMPERATURE NOTTO SUBSTANTIALLY EXCEED ABOUT 240*F.
 2. The improvement defined in claim1 wherein said heat is directed upon said inner surface for apredetermined period of time not to substantially exceed about 3minutes.